awk version of the script has an inherent issue when dealing with 64-bit
addresses: all numeric values are internally stored as doubles by awk. This
causes severe loss of precision with high 64-bit values.
Rewrite it in Lua which is much better suited for dealing with binary data
and change the name to a more generic one (kernel_boothdr.lua) because of
the newly added RISC-V booti header generation support.